How to price a fixed project
Price = (estimated hours × (1 + contingency) × hourly rate + costs) × (1 + markup). VAT or sales tax is added on top where you're registered. Projects almost always take longer than estimated, so a 10–25% buffer protects your effective rate.
The effective rate shows what you earn per originally estimated hour if the work goes to plan. Ask for a deposit (30–50% is common) before starting.